This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The hemeprotein neuroglobin (Ngb) is a recently discovered member of the globin family, that is expressed in the nervous system of humans and other vertebrates, and is involved in the protection of the brain from ischemic damage. Despite considerable interest, the precise in vivo function is still unknown. The x-ray diffraction (XRD) structure of the murine wild type, ferric bis-histidine form (at 1.4 [unreadable] resol.) and the ferrous CO-bound form (at 1.7 [unreadable] resol.) are known. In this project, we propose to perform a study of polarized x-ray absorption fine structure (XAFS) spectroscopy of these Ngb single crystals. In fact, due to the position of the hemes in the unit cell of these protein crystals, the x-ray polarization vector can be oriented nearly parallel to the heme planes or to the heme normals: these so called polarized XAFS spectra allow both a check/refinement of the XRD data and a comparison with the XAFS results obtained in solution, The possibility to determine with high accuracy the active site of this protein in these two forms may be of interest to clarify the still debated function of Ngb: although Ngb has an overall structure which is similar to myoglobin, the fine regulation of ligand binding depends on proximal coordination and distal constraints in a way that is very different from the canonical oxygen storage mechanism of myoglobin. The polarized XAFS study proposed here is expected to yield a deeper structural description of the details associated to the ligand binding mechanism and will eventually help to clarify the function and biological role of Ngb.